The carmaker said the move was the “result of many months of close collaboration” with the Environmental Protection Agency and the California Air Resources Board. Fiat Chrysler said it thought the updates would help it reach settlements with the E.P.A. and the Justice Department.
The Justice Department has been investigating Fiat Chrysler since the E.P.A. in January accused the carmaker of violating clean-air rules. Fiat Chrysler said this week that it was trying to work out a settlement with the Justice Department, but added that it would fight any suggestion that it had used illegal software to dupe regulators.
In 2015 and 2016, the company sold more than 50,000 diesel Ram pickups in the United States each year, making the model the country’s largest-selling diesel-powered light vehicle by far, according to HybridCars.com. But the emissions question has kept Fiat Chrysler from selling any diesel Ram or Grand Cherokee vehicles this year because the E.P.A. has not certified them for sale.
The E.P.A. declined to comment about Fiat Chrysler’s announcement.
The company already faces accusations in Europe that its cars produce far more nitrogen oxides in normal driving than during tests. On Wednesday, the European Union’s executive arm filed a formal complaint against the Italian government for allowing Fiat Chrysler to sell cars designed to evade emissions tests.
And the evidence has piled up that those high emissions levels were part of efforts to evade environmental standards.
Academic researchers on both sides of the Atlantic said separately this week that they had found that Fiat Chrysler’s diesel vehicles had suspiciously high pollution levels and that there was evidence the company had used a so-called defeat device, software intended to allow a vehicle to pass official emissions tests but to pollute more when driven on the…